Troubleshooting "OL"
3. Common Culprits Behind Unexpected "OL" Readings
Okay, so you're getting "OL," but something feels fishy. The insulation shouldn't be that good, or you're testing something where high resistance just doesn't make sense. What now? Time to put on your detective hat and start sleuthing.
First, check those test leads! Are they properly connected? Are they damaged or corroded? A faulty connection can easily lead to a false "OL" reading. Think of it as trying to whisper across a crowded room; if the connection is bad, the message (in this case, the resistance measurement) won't get through properly.
Next, consider the environment. High humidity can significantly impact insulation resistance, especially on older or damaged insulation. Moisture provides a conductive path, effectively lowering the resistance. Also, temperature plays a role; resistance generally decreases as temperature increases. So, if you're testing in a sauna, expect different results than if you're testing in a freezer (though, why would you be testing in a freezer?).
Finally, don't rule out the Megger itself. A low battery can cause erratic readings, including "OL." Try replacing the battery or using an external power supply. Also, make sure the Megger is calibrated properly. If it's been a while since its last calibration, it might be giving inaccurate readings. It's like using a warped measuring tape; you're not going to get accurate results.